Lost Circulation Prevention & Mitigation
Challenge:
Lost circulation occurs when drilling fluid is lost to the formation through porous, vugular or fractured formations. Fractures can be natural, or induced by the drilling process, especially when poor drilling practices are evident. In many drilling environments, lost circulation control is critical. For instance, in deepwater, losses more easily occur due to the narrow pore pressure/fracture gradient windows, colder drilling fluid temperatures, and high equivalent circulating densities (ECD). At the same time, the financial impact of losses is high due to the high cost per barrel of synthetic and mineral based fluids and the high spread cost of a deepwater drilling project.
If the tight fracture gradient/ECD window is not properly managed, the formation can break down, leading to lost circulation and well control situations. In addition, drilling a wellbore alters the stress distribution in the localized area around the wellbore. These stresses can cause micro-fractures, which, if not stabilized and sealed, through Mechanical Wellbore Stabilization, they can propagate, and grow. Once losses occur, the focus is re-directed from prevention to lost circulation mitigation and then remediation. Losses can range from seepage to severe whole mud losses, with solutions varying depending upon degree.
Solutions:
Mechanical Wellbore Stabilization: When drilling zones with expected losses, stresses can be relieved by propping and sealing mircofractures in the formation with the use of Mechanical Wellbore Stabilization products. As fractures are induced, the sized-particle blends propagate the fracture; plug the pore throat, then seal the fracture tip. This effectively arrests fracture propagation and wellbore instability.
- Newpark’s new Mechanical Wellbore Stability suite of products, which includes the PreFIX wellbore sealant and ProppFIX and FracFIX proppant blends, is especially designed to strengthen and seal fractures in the wellbore.
ECD Management: When drilling through depleted zones in the deepwater environment, having a fluid with a low equivalent circulating density (ECD) is mandatory in the management of extremely narrow fracture gradient windows, especially when drilling a wellbore of 9-7/8”, or narrower. The ECD is the density that reflects the pressure that is actually imposed on the wellbore during circulation. It includes the mud weight, the friction pressures on the annulus as the fluid circulates, and by cuttings loading when drilling. Low-ECD fluids are used because they are designed to minimize pressure losses, and optimize flow rates.
- Newpark’s Kronos™ low-ECD system is designed specifically to reduce ECD spike magnitude through minimization of pressure losses and optimization of flow rates. These characteristics are achieved at any given fluid density by lowering the overall rheological characteristics of the fluid while minimizing sag potential. The Kronos Low-ECD system is appropriate for deeper well sections with narrow wellbore diameters. Kronos systems are stable over a wide range of temperature and pressure.
Lost Circulation Mitigation and Remediation: Solutions for lost circulation vary depending on the seriousness of the event, which ranges from seepage losses, to partial losses, and finally, total loss of returns. Lost circulation materials (LCM) are often delivered to the loss zone in sweeps and/or squeeze pills. A wide distribution of particle size, and types, can improve success. Total losses are remediated with Newpark’s X-Prima, high solids, high fluid loss squeeze.
Water-based Fluid Solutions: Water-based drilling fluids such as Newpark’s Evolution and DeepDrill drilling fluid systems, often present an advantage over non-aqueous fluids, in that their base-fluid, water or brine, is not compressible. If a drilling fluid compresses under pressure, the volume of barite increases in comparison to the volume of drilling fluid, thereby increasing the mud weight of the fluid. That can be enough to fracture the formation.
High Performance Brine Drilling Fluid Proves Cost Effective in Eagle Ford Shale: In many areas of the Eagle Ford Shale, lost circulation is a common cause of lost time and increased well cost. The Austin Chalk, above the Eagle Ford, is a depleted zone. Losses are common. A high performance produced brine system is a cost effective alternative to diesel oil-based fluids.
DeepDrill System Eliminates Losses, Improves Logging in Deepwater Gulf of Mexico: An operator planned to drill a well in Green Canyon 82. On previous wells in that block, the operator experienced significant losses of synthetic-based fluid in the intermediate section. The current well plan included an extensive formation evaluation program at total depth, which would necessitate leaving the wellbore exposed for several days while logging and coring.